Arboriculture & Urban Forestry 32(3): May 2006 101 rust (Puccinia, Uromyces spp.), gray mold (Botrytis cinerea Pers.), eyespot (Septoria nodorum Berk.), and leaf spot (Py- renophora spp.), economically important diseases of cereals, vegetables, fruit, and ornamentals (Marco et al. 1994; Suther- land and Walters 2001, 2002). Little scientific investigation into film-forming polymers to control foliar diseases of urban trees has occurred. Consequently, the aim of this study was to determine the effect of four commercially available film- forming polymers on Guignardia leaf blotch of horsechestnut and powdery mildew infection of English oak. MATERIALS AND METHODS Plant Material and Experimental Design The experiment used 3-year-old, bare-rooted stock of horsechestnut (Aesculus hippocastanum L.) and English oak (Quercus robur L.) obtained from a local supplier. Trees were planted directly into the ground by hand in early November 2001 and left to establish throughout the 2002 and 2003 growing season. The trial site was located at the University of Reading Shinfield Experimental Site, Berkshire. Planting dis- tances were1×1m (3.3 × 3.3 ft). Supplementary irrigation was applied during the 2002 and 2003 growing season, and trees were fertilized annually via a broadcast application of granular N:P:K (29:7:9) fertilizer (Bartlett BOOST, Doggett Corp., Lebanon, NJ) applied at 40 g/m2 (1.4 oz/11 ft2) in early May. No watering or fertilization was applied during the 2004 trial. The soil was a sandy loam containing 4% to 6% organic matter, pH 6.2; available P, K, Mg, Na, and Ca levels were 52, 659.1, 175.2, 49.4, and 2188 mg/L (0.0001, 0.005, 0.002, 0.0001, 0.02 oz/gallon), respectively, at the time treatments commenced (May 2004). Weeds were con- trolled chemically using glyphosate (Roundup; Green-Tech, Sweethills Park, Nun Monkton, York) from the day of plant- ing, November 2001, to the cessation of the experiment, Sep- tember 2004. Historically, both horsechestnut and English oak suffered heavily from Guignardia leaf blotch and powdery mildew infection, respectively, on an annual basis. Consequently, prior to the trial commencing in 2004, trees were inspected in September 2003, and only those trees rated with a disease severity of 4 (51% to 80% of leaves affected, severe foliar discoloration) were used in the trial. A minimal insecticide program based on the residual pyrethroid insecticide delta- methrin (Bandu, Headland Agrochemicals Ltd., Saffron Wal- den, Essex) was applied every 3 months during each growing season commencing in May 2002 to September 2004. All sprays were applied using a Tom Wanner Spray Rig sprayer at 40 mL (1.2 fl oz) deltamethrin (Bandu) per 100 L (26 gal) of water. Trees were sprayed until runoff, generally 0.25 L (0.07 gal) insecticide per tree. The experimental design was a randomized complete block with five single-tree replications. All treatments commenced under field conditions in early May 2004, when both test species were in full leaf, and treatments were repeated in early June. To keep the physiological age of the leaves com- parable throughout the experiment, measurements of chloro- phyll fluorescence and chlorophyll content (SPAD) were made only on fully expanded 21 to 28 day old leaves. In all cases, chlorophyll fluorescence and SPAD measurements were taken from six leaves (two from the top of the crown, two in the center, and two at the base) per tree. Leaves were tagged to ensure that the same leaves were measured through- out the experimental period. Treatments Prior to film-forming polymer sprays, polythene screens 1 m (3.3 ft) high were erected around each tree to prevent dis- persal of sprays and possible cross-contact with other trees, and the base of the tree was covered with a 0.5 × 0.5 m (1.65 × 1.65 ft) polythene mulch to prevent percolation into the soil. Film-Forming Polymers Foliar sprays of the film-forming polymers Bond (active in- gredient [a.i.] alkyl phenyl hydroxyl polyoxyehtylene), De- signer (a.i. styrene-butadiene copolymer + polyalkylene ox- ide modified heptamethyl trisiloxane), Nu-Film P (a.i. poly- 1-p menthene), and Spray Gard (a.i. di-1-p menthene) were applied until runoff using a hand-sprayer at a concentration of 10 mL (0.3 fl oz) per liter (0.26 gal) of water. Ten mL (0.3 fl oz) per liter (0.26 gal) of water was selected as a foliar spray concentration based on results of a preliminary trial to deter- mine the maximal concentration of film-forming polymer that could be applied to leaf tissue without the onset of phytotox- icity damage (data not shown). All film-forming polymers were obtained from United Agri Products Ltd. (Alconbury Weston, Huntingdon). In addition, a comparative evaluation of the fungicide Topas (a.i. penconazole), a protectant cona- zole fungicide with antisporulant activity (Syngenta Crop Protection UK Ltd., Whittlesford, Cambridge), commercially used for powdery mildew control, was conducted by spraying trees at the manufacturer’s recommended rate of 1.5 mL (0.045 fl oz) per liter (0.26 gal) of water. Chlorophyll Fluorescence Fluorescence values were obtained by placing leaves in dark- ness for 30 min by attaching light exclusion clips to the leaf surface of whole trees, and chlorophyll fluorescence was measured using a HandyPEA portable fluorescence spec- trometer (Hansatech Instruments Ltd., King’s Lynn). Mea- surements were recorded up to 1 sec with a data acquisition rate of 10 s for the first 2 ms and of 1 ms thereafter. The fluorescence responses were induced by a red (peak at 660 nm) light of 1500 mol m−2 s−1 photosynthetically active radiation (PAR) intensity provided by an array of six red light-emitting diodes. The ratio of variable (Fv Fm − Fo) to maximal (Fm) fluorescence (i.e., Fv/Fm), which represents ©2006 International Society of Arboriculture
May 2006
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